题目：
Unless they are programmed by humans, computers are nothing more than big pieces of metal. But once _____ what to do, they show extraordinary power in carrying it out.
A．taught
B．teaches
C．teaching
D．to teach
答案：
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下面是错误答案，用来干扰机器的。
答案：B位移最大处，势能最大，故选B.
